Soil-structure interaction during the San Fernando earthquake

Accelerograms obtained at two sites during the San Fernando earthquake of 1971 were analyzed to investigate the role of soil-structure interaction, using techniques developed by Bielak and others. Analysis of the data from the site of the Hollywood Storage Building, for which data from the Arvin-Tehachapi earthquake of 1952 are also available, showed evidence of soil-structure interaction in the way the transfer functions between parking lot and basement motion decayed with increasing frequency in the two lateral directions. It is concluded also that interaction probably had a small effect on the response near the EW fundamental frequency during the San Fernando earthquake. Although theoretical and experimentally determined transfer functions are broadly similar, they do not agree in detail. The lack of good agreement for reasonable choices of the parameters of the theoretical model indicates a need for some modifications of the theory or its application, and a need for more measurements at the site. A similar analysis showed no clear evidence of soil-structure interaction for the Millikan Library and Athanaeum buildings on the campus of the California Institute of Technology. If soil-structure interaction caused the major differences measured in the base motions of these two buildings, it is of a more complex form than that considered by present theories

Centrifuge liquefaction tests in a laminar box

The difficulties associated with instrumenting earthquake sites in order to record pore pressure changes in a future event led to the use of scaled model tests performed in a centrifuge. Both dry and saturated sands were employed, contained in a box constructed of aluminium laminae designed to move freely on each other. This would result in shearing distortions developing in the soil unimpeded by the container. Accelerometers, displacement transducers and pore pressure sensors were attached to the box and embedded in the soil at various elevations so as to record the response of the soil to an earthquake-like excitation supplied to the base of the container. A special apparatus was constructed to imitate earthquake motion. In some tests on saturated sand, the soil profile was liquefied. Test results of accelerations, lateral and vertical displacements and pore pressures against time for typical earthquake inputs are given. The data, obtained under controlled conditions, can be compared with the various calculation methods for dynamically generated pore pressures

Engineering studies of the San Fernando earthquake

A number of accelerograms obtained during the San Fernando earthquake were analyzed to investigate the nature of the strong motion. The particular features studied were soil-structure interaction and the relative influence of local site conditions versus the source mechanism and travel paths of earthquake waves. Evidence of soil-structure interaction in the EW fundamental mode of the Hollywood Storage building is seen in the earthquake data. General agreement exists up to - 5 c.p.s. in both lateral directions between theoretical, base to free field transfer functions and transfer functions derived from accelerograms obtained in the basement and adjacent parking lot. There was no evidence of soil-structure interaction in the Millikan Library and Athenaeum buildings on the Caltech campus, and this effect could not account for the major differences in their accelerograms. Accelerogram, Fourier Amplitude Spectra, and Response Spectra data were compared from a group of six tall buildings close together near Wilshire Blvd. and Normandie Ave. in Los Angeles and from seven surrounding buildings, two to three miles away. The data indicated that local site conditions and soll-structure interaction were not major contributors to the observed differences in the response at these sites. There was correlation between the degree of similarity in the response at two sites and their distance apart. A simple wave superposition model with numerical examples confirms this correlation

Vibration Analysis of Rotating Fans Mounted on Adjacent Rectangular Foundation Blocks

Vibration analysis was conducted for large rotating fans mounted on adjacent rectangular concrete foundation blocks, 66 ft x 22 ft x 10 ft depth, with the adjacent long sides 10 ft apart. The blocks were embedded in medium dense sands and gravels with a variable shear-wave velocity profile. The purpose of the analysis was to determine whether (1) the dynamic interaction of the blocks through the surrounding soil would cause unacceptable vibratory response of the fans, and (2) the foundation stiffness criterion set by the vendor was satisfied. Solutions were obtained using the 3-D dynamic version of the FLAC computer program, which was first used to compute the response of a single block-fan system. The introduction of the second block-fan system into the model resulted in less than 10% amplification in dynamic response of the two-block system relative to the single block-fan response, when the excitation forces of both fans were in phase (i.e. 0° lag). However, a maximum amplification of 100% was computed when the phase-angle difference in forces was between approximately 90° and 120°. The results ultimately demonstrated that the vibration and foundation stiffness criteria could be met, which would have been more difficult without the use of a 3-D numerical modeling code

Model Identification and Seismic Analysis of Meloland Road Overcrossing

This report presents the results of research directed toward model identification and seismic analysis of the MRO. This research has been implemented to meet the requirements of Tasks 4 and 5 of the UNR-D&M research program (Sec. 1.1.3) and also to provide a basis for developing improved bridge modeling procedures as required under the D & M research program on SBOs (Sec. 1.1.4). The scope of this research effort consisted of our development of a finite element model of the MRO whose parameters were estimated through the application of state-of-the-art system identification methods to the MRO's recorded motions from the Imperial Valley Earthquake. These estimated model parameters were also checked for consistency with an overall range of model parameter values computed using established engineering procedures. This model was then used in a series of parametric dynamic analyses of the seismic response of the MRO which enabled us to evaluate the effects of uncertainties in the various model parameters on the demand forces and moments in the structural members and the foundation springs. Maximum foundation spring forces and moments obtained from these analyses were used as input to nonlinear static analyses of the MRO's pile foundations in order to compute the demand forces and moments within the piles. The demand forces and moments within the MRO's structural and pile elements were then compared against the capacities of these elements. These analysis results have been interpreted to assess the seismic performance and design of the MRO, and also to provide an important basis for our development of improved modeling and seismic evaluation procedures for short bridge overcrossing structures. The above efforts have focused on the modeling and analysis of the MRO's translational and rotational response to transverse horizontal input motions; i.e., the bridge's response to vertical and longitudinal input motions was not included in this research. This focus on the MRO's response to transverse horizontal input motions was adopted because: (a) this response will lead to more severe earthquake-induced internal forces and moments, particularly in the central pier which is the element of an SBO that is typically most vulnerable to seismic excitation; and (b) our past evaluations of the MRO's recorded motions have shown that its response to transverse horizontal input motions is strongly affected by SSI, whereas SSI has only a negligible effect of the MRO's response to vertical and longitudinal input motions (Werner, et. al., 1987)

Analysis and Testing of the FBA-11 Force [Balance] Accelerometer

The FBA-11 is a feedback-controlled accelerometer widely used to measure and record accelerations arising from earthquakes. It has found application both for structural response and for ground motion studies. The design intent of the FBA-11 was to provide electronic control of the natural frequency, damping, and output voltage. Included in this paper are (1) a circuit analysis yielding the complete closed-loop transfer function, and (2) the corroborative test results from shake table evaluations. The transfer function can be used to correct recorded accelerations for instrument response

Seismic Performance Evaluation of a Submarine Gas Pipeline

Analyses were conducted on the seismic performance of a proposed offshore gas flowline, which connects a manifold in 830-m water depth to a riser platform in shallow waters of the outer continental shelf. Climbing a 10-degree continental slope, the flowline will be installed on the seafloor underlain by deep carbonate sediments of sands and silty clays. Two types of analyses were performed for a critical segment of the flowline, where it traverses a narrow ridge flanked by two deep submarine canyons: (1) probabilistic analyses using simplified empirical methods; and (2) deterministic 2D and 3D analyses with FLAC using a nonlinear, effective-stress soil model fully coupled with an empirical pore-pressure generation scheme. Soil properties were derived from PCPT and T-bar data, Bender element tests, and monotonic and cyclic direct simple shear tests. The analysis results indicated an extremely small likelihood of liquefaction along the flowline, with only small deformations predicted to occur for ground motions with a return period of 5,000 years

LIPOGENESIS IN ADIPOSE TISSUE FROM OVARIECTOMIZED AND INTACT HEIFERS IMMUNIZED AGAINST ESTRADIOL AND(OR) IMPLANTED WITH TRENBOLONE ACETATE

Forty-two heifers were allotted randomly to six treatment groups: 1) intact controls, 2) intact heifers implanted with trenbolone acetate, 3) ovariectomized heifers, 4) ovariectomized heifers implanted with trenbolone acetate, 5) intact heifers immunized against estradiol and 6) intact heifers immunized against estradiol and implanted with trenbolone acetate. Blood titers of estradiol-17β were increased over lO0-fold in heifers immunized against estradiol in Freund\u27s complete adjuvant or saline:squalene/arlacel containing Mycobacterium. Lipogenic enzyme activities and acetate incorporation into fatty acids were increased in subcutaneous adipose tissue obtained at slaughter from heifers receiving immunization or the combination of immunization and trenbolone acetate. The increased lipogenic capacity was not reflected in either cell diameter or cells per gram adipose tissue. Ovariectomy in combination with trenbolone acetate caused the lowest activities for all enzymes measured. This treatments also caused the greatest decrease in cell diameter, which resulted in the largest number of cells per gram of adipose tissue. Trenbotone acetate alone had no detectable effect on lipogenesis in the intact heifer, but the combination of ovariectomy and trenbolone acetate caused substantial decreases in enzyme activities, in most cases a significant decrease as compared with ovariectomized heifers. The data suggest that trenbolone acetate is able to depress lipogenesis only when not competing with the effects of circulating estradiol

LIPOGENESIS IN ADIPOSE TISSUE FROM OVARIECTOMIZED AND INTACT HEIFERS IMMUNIZED AGAINST ESTRADIOL AND(OR) IMPLANTED WITH TRENBOLONE ACETATE

Forty-two heifers were allotted randomly to six treatment groups: 1) intact controls, 2) intact heifers implanted with trenbolone acetate, 3) ovariectomized heifers, 4) ovariectomized heifers implanted with trenbolone acetate, 5) intact heifers immunized against estradiol and 6) intact heifers immunized against estradiol and implanted with trenbolone acetate. Blood titers of estradiol-17β were increased over lO0-fold in heifers immunized against estradiol in Freund\u27s complete adjuvant or saline:squalene/arlacel containing Mycobacterium. Lipogenic enzyme activities and acetate incorporation into fatty acids were increased in subcutaneous adipose tissue obtained at slaughter from heifers receiving immunization or the combination of immunization and trenbolone acetate. The increased lipogenic capacity was not reflected in either cell diameter or cells per gram adipose tissue. Ovariectomy in combination with trenbolone acetate caused the lowest activities for all enzymes measured. This treatments also caused the greatest decrease in cell diameter, which resulted in the largest number of cells per gram of adipose tissue. Trenbotone acetate alone had no detectable effect on lipogenesis in the intact heifer, but the combination of ovariectomy and trenbolone acetate caused substantial decreases in enzyme activities, in most cases a significant decrease as compared with ovariectomized heifers. The data suggest that trenbolone acetate is able to depress lipogenesis only when not competing with the effects of circulating estradiol